Hammer looked somewhat annoyed, and his annoyance immediately surfaced on his face, appearing quite intense.
Hammer intended to control the survival time of that major to about half an hour, letting the doctors attempt to save him for half an hour before finally succumbing. There wasn't a special reason for doing so, it was just what he wanted.
Disguising it as an accident while ensuring the target can't speak alive is sometimes crucial. If the rescued is heavily injured but survives, people feel it's an accident, but once dead, suspicions arise. However, this time, such measures weren't necessary at all.
In plain terms, Hammer just had an itch to scratch.
So Hammer was very annoyed why the colonel died after just ten minutes instead of lasting the intended half hour. It illustrated his technique had regressed, as his control over the force wasn't as precise as it used to be.
So, Hammer was genuinely upset.
